Cutting torch machine



Dec. 12, 1944. Mon ET AL 2,364,644

CUTTING TORCH MACHINE Filed April 4, 1941 5 Sheets-Sheet 1 KO u: q E N N1 I I EE'E 5 3 335 9 5 POSITION FOR NORMAL PLATE mmou Fnn swam FOR

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BEVELS CURVES ETC RAVEL MINUTE TORCH TRAVEL FEET PER HOUR CUTTING TIPSIZE LBS. PER sq. INCH TORCH 1' IN PER ATTORNEYS Filed April 4, 1941 3Sheets-Sheet 2 2 .J S .J 5 5 0 0 WWW W m w a W m a 3 0 2 2 0 -0 Q 2 00QQQQQQQQ m ww xw Q QQ Q Q5 www R m Q Q Q w w DUDDUDDDDDDD AIL Dec. 12,1944. c. MOTT ET AL 2,364,644

CUTTING TORCH MACHINE Filed 451 4, 1941 3 Sheets-Sheet sSynChrOIZOllSMOi'OT'SiIZjlGPMSG I lq.E

PRE-AMPLIFIER POWER-AMPLIFIER TO PETE-AMPLIFIER FREQUENCY ATTORNEYSPatented Dec. 12, 1944 2,364,644; CUTTING TORCH MACHINE Chester Mott,Evanston, Chicago, Ill., assignors Company, Chicago, Ill

ware

and Alfred F. Chouinard, to National Cylinder Gas a corporation o1 Dela-Application April 4, 1941, Serial No. 386,874

ill Claims.

The present invention relates tomeans for selectively controlling the'speed of such motors in torch cutting machines for controlling the rateof cutting.

in torch cutting machines it is common practice to mount theoxy-acetylene cutting torch on a carriage, and to propel the carriage,and propel the torch along the carriage by an electric motor whichdrives a traction wheel, having guided with the that speed should bekept constant. If it be too fast,- the cut will not be completelythrough the plate; if it is too slow, an excessive amount of metal willbe burned away, and the cut will be too wide; and if the speed varies,the cut will be irregular in width and the out incomplete in places. a

The speed of an ordinary series-wound electric motor may be controlledwithin general limits by but this peed cannot be kept constant withinclose limim by the rheostat or any other known means. With any givenrheostat setting, the speed of the motor will vary with fluctuations inload; variations in the amount of current tapped oil the line by otherelectrical equipment in the plant; warming up of the motor which changesthe conductivity of the coils; warming up of the lubricating oil, whichreduces its viscosity; and various other factors.

A synchronous motor will hold a definite and fixed speed, but that speedis one determined by the builder of the motor, (1. e. by the number ofpoles), and by the frequency of the current available, which isordinarily (50 cycles, and this speed cannot be altered or modified bythe user. There are some exceptions, for instance, where the motor is ofthe muiti-pole type, and certain poles may be cut out of the circuit,but any such cutting in or out of the poles does not permit more than avery small number of speed changes, and does not permit any smallpreselected variations.

it is possible to operate asychronous motor at one definite speed andobtain various required output speeds by mean of mechanical gearing. Thedrawbacks to this method are loss of power through friction in thegearing, and the fact that considerably more space is required toaccommediate the gearing and the gear shifting mechanism than isrequired to accommodate the synchronous motor, especially if the rangeof speeds is large.

One object of the present invention is to provide means for operatingthe synchronous motor of a torch cutting machinethrough a wide range ofselective speeds by changing the frequency of the current impressed onsaid motor.

Another object is to provide means for operating the drive motor of atorch cutting machine through a wide range of selective speeds, whilemaintaining any chosen speed at an extremely high degree of constancy.Another object is to provide means for selectively changing the speed ofthe drive unit of a torch cutting machine automatically according to thesetting of a chart device, indexed with various plate thicknesses.

Another object is to provide a new and improved cutting calculator chartdevice, affording an indicating the correct values and view of a devicefor changing the current operating the synchronous drive motor of atorch cutting machine.

Fig. 3 .is a fragmentary plan view of a disc,

forming part of the device for changing the frequency of the current tothe synchronous drive form of disc.

Fig. 5 is a face view of the control chart on a larger scale than inFig. 2.

Fig. 6 is a somewhat diagrammatic showing of a wiring diagram by meansof which the speed of the synchronous drive motor of a torch cuttingmachine can be selectively changed.

Fig. '7 is a somewhat diagrammatic section showing a circuit controllerforming a part of the electrical system of Fig. 6.

Fig. 8 is a section taken on line and Fig. 9 is a curve showing theoutput voltagefrequency characteristics of the current produced by theelectrical system of Fig. 6.

As an example of a type of torch cutting machine in which our inventionmay be employed,

38 of Fig. 7,

we have shown somewhat schematically in Fig. l

a cutting apparatus having a carriage H], which travels horizontally onrails Mia over a table l2, on which may be supported a templet, drawing,pattern or other guide. A. drive unit it, which may be of any well knowntype, or which may be of the form shown and claimed in applicants Patent2,336,626, issued December 14, 1943, on an application copendingherewith, is supported on carriage ID for horizontal movement therealongcrosswise of the movement of said carriage. This I drive unit l3 has atracing element id in the form of a tracer wheel, pointer, spot oflight, or the like, which can be steered along the outline of thepatternor other guide to be copied or traced. This tracing element ismay be in the form of a traction wheel driven from a motor I6 (Figs. 1aand 6) forming part of the movable unit l3, or a separate traction wheelmay be provided driven from said motor. The traction wheel on the unitit is driven from the motor is as the tracing element i4 is steered overthe table 12, to cause the movement of the carriage i0 along its rails,and the movement of said unit along said carriage.

One Or more torch units ii are supported on the carriage it, and areconnected to the drive unit l3 for movement therewith along saidcarriage and over the plate is to be cut, so that the cutting speed ofthese units corresponds to the speed of the traction wheel and itsdirectly connected drive motor iii. These torch units i1 may be of anysuitable well known construction, or may be of the form shown andclaimed in the Chouinard Patent 2,336,596, issued December 14, 1943, onan application copending herewith.

As a feature of the present invention, the drive motor i6 is of thesynchronous type, and the frequency of the current supplied thereto ischanged in accordance with the desired cutting speed of the torches 20.This change in frequency is effected by creating periodic currentpulsations at selective frequencies depending on the desired torchcutting speed, and amplifying these pulsations to a value necessary tooperate the synchronous motor In. The construction and arrangements ofparts so far as concerns the controlling of the synchronous motor, whenused for purposes other than in connection with and as a part of thepresent application, are claimed in applicants divisional applicationSerial No. 522,566, filed February 16, 1944.

One form of construction for obtaining current pulsations of selectivefrequencies is shown in Figs. 2 and 3, and comprises a disc 22, which isprovided with a plurality of concentric annular series or rows ofalternate opaque segments 23, and light transmitting segments 24, andwhich is driven at constant speed from a synchronous motor 25 throughsuitable reduction gearing.

The light transmitting segments 24 may constitute slots in an opaquedisc, or the disc 22 may be of glass or other suitable transparentmaterial, coated or fired with a black pigment, or otherwise renderedopaque at all sections except at the light transmitting sections 24.

A source of light 26 shown in the form of an exciter lamp, and a lightreactive device 21 shown in the form of a shielded photo-electric cellare disposed on opposite sides of the disc 22, and are movable in unisonradially of said disc into registry with any selective row of lighttransmitting segments 24. When one of thesesegments 24 moves intoregistry with the line of light between the lamp 26, and the aperture21a of the shield around the photo-electric cell 21, current isgenerated in said cell, and when an opaque segment 23 moves into saidline of light, the generation of current in said cell stops. As aresult, there is generated in the photo-electric cell 21 a pulsatingcurrent having a frequency depending on the number of light transmittingsegments 24 in the registering row, brought into and out of position perunit of time.

The number of light transmitting segments 24 in each row variesaccording to the desired speed of the motor IS and therefore of thetorch. For instance the inner row may have ten transparent sections 24and ten opaque sections 23 alternately arranged. With the disc 22 makingtwo revolutions per second, the frequency obtained by the inner row is28 cycles per second (one transparent and one opaque sectionconstituting one cycle). The next row may be arranged to generate 22cycles, the following row 24 cycles, and so on up to the outer row whichmay be arranged to generate 400 cycles. With this range of availablefrequency it is possible to vary the speed of the cutting torches from 2to 40 inches per minute to cut plates ranging from the thinnest to thethickest.

Instead of providing well defined alternate opaque and transparentsection 23 and 24 as shown in Fig. 3, it i preferable to make the discas shown in Fig. 4, with the light transmitting sections 24a graded fromabsolute transparency to absolute opacity, to produce sinusoidal orsimilar form of undulated pulsations.

As far as certain aspects of the present invention are concerned, othermeans may be provided for obtaining current of selective frequencies.For instance, alternatin current may be induced in a coil by means of asteel disc having a plurality of annular rows of slots. With the coilopposite one of said rows, current will be induced therein when'thesolid parts of the disc pass opposite said coil, the induced currentdiminishing to zero as the slots pass opposite said coil.

Also as far a certain aspects of th invention are concerned, a standardtype of signal generator well known in the art can be employed to obtainminute current pulsations of selective frequency.

As a feature of the present invention, the change in frequency of thecurrent to the motor I6 is effected automatically upon the setting of acutting calculator chart device indexed with various plate thicknessesand mounted on carriage ill. This chart device indicates the correctvalues and adjustments required for each parp ticular thickness of platebeingcut with a particularized torch and tip, and is adjustable tocompensate for conditions which influence these values. For that purposethe chart device comprises a lower stationary .chart section 33, and anupper chart section 3|, adiustably movable along the upper edge thereof,and provided with a horizontal row of'figures indicating platethicknesses. The lower chart has a plurality of horizontal tabulationscontaining cutting data corresponding to respective plate thicknessesindicated -in' the upper chart section 3|. This data may inelude speedof torch travel in feet per hour, or inches per minute, or feetpersecond, or both,

cutting tip sizes, cutting oxygen pressure, and

, cubic feet of cutting oxygen consumed per foot of cut.

The proper cutting speed for a plate of a deflnite thickness depends onthe shape of the cut, and various conditions of the plate. For instance,in making cuts having sharp corners, bevelsor curves, the speed of thecutting torch should be decreased. If the plate is warm then the cuttingspeed should be increased, if cold it should be decreased, and if theplate has a considerable amount of scale on its surface, or is extraclean, the lineal cutting speed should be reduced or increasedaccordingly.

In order to adjust the chart device for these unusual conditions, thereis provided on the upper chart section 3| a scale having an index orpointer 32, and the'lower chart section 33 has a scale comprising a'mainpointer 33, and a series of auxiliary pointers 34 on opposite sides ofsaid main pointer. When the two pointers 32 and 33 are in registry, thechart is set for normal plate conditions. By sliding the upper chartsection 3| to effect registry of the pointer 32 with any one of thauxiliary pointers 34 in the lower chart section 33, the chart iscorrected for abnormal conditions.

The slidable adjusting movement of the upper chart section 3| may beeffected through a hand wheel 33 (see Fig. 1) supported on the carriage10, and. accessible for operation from the front of said carriage. Thetron from the hand wheel 33' is shown comprising a pinion 31 (see Fig.2) fixed to the hand wheel shaft, and meshing with rack teeth 33 alongoneedge of the upper chart section 3|.

an indicator slide 43 is movable across the face of the chart sections33 and 3| into registry with that figure in the upper chart section 3|indicating the thickness of the/plate to be cut, and is desirably in theform of a slotted bar or a vertical looped wire, which when moved intoregistry with said figure, lines up and encloses the correcarriage l3,and accessible for operation from the front of said carriage. The tronbetween this hand wheel and the slide 43 may be of any desired type. Iti shown as including a bevel gear 42, mounted on the shaft 43 of thehandle 4|, and me. with a bevel gear 44 secured to an axially fix leadscrew 43. Threaded on the lead screw 43 is a nut 43 to which is affixedan arm 41 rigid with the slide 43.

In order to correspondingly position the light source 23 and lightreactive device 21 with respect to the slide 43, there is provided asecond axially fixed lead screw 43, driven from the lead screw 43through intermeshing gears 33, 3| and 32, and carrying a nut 33, securedto a yoke 34,

with side arms carrying the members 23 and 21.

When the handle 4| is turned to set the slide 43 on the chart 3| inaccordance with the thickness of the plate to be cut, the frequencycontrol device is automatically set to deliver the proper frequency tothe pre-amplifler and ultimately drive the synchronous motor I3, thusobtaining the proper torch speed for said plates.

In order to insure that the members 23 and 21 are stopped in properalignment with the desired frequency control ring on the disc 22, thereis provided an index device which may comprise a cam 35, secured to thelead screw 43 for rotation therewith, and provided with one or morerecesses 33. A roller 51 carried on a pivot arm 33 is urged against theperiphery of the cam by a spring 33. When the roller 51 is in one of therecesses 33, the light 23 and the light reactive device 21 will be inproper alignment with one of the frequency control rows. The operatorcan tell when this position is reached by the feel of the handle 4| asit turns easily into correct position, and greater resistance isencountered in moving it out of correct position.

All of the parts shown in Fig. 2 are mounted on the carriage. The chartsections 33, 3|, slide 43, and handles 33 and 4| are on the front sideof the carriage, while the remaining parts are mounted on the rear sideof the carriage and preferably in a suitable casing or housing. Tofacilitate a clear showing of the parts appearing in Fig. 2, they havebeen spread apart, and in synchronous motor l3. In this system, the maininput lines A are connected to a commercial source of alternatingcurrent-which is usually 30 cycles, 115 volts.

Low voltage circuit The current is branched off from point 1| on oneline of the main to points 12 and 13, and through various transformersof a power amplifier B of well known construction to reduce the voltageto values suitable for operation of the tube filaments in saidamplifier, and also to supply power to the tubes in a pre-amplifier C ofwell known construction. The current then returns to points 14 and 13,and then to point 13 on the other line of the main.

Current flows out p of the pre-amplifier C at point 33 and passesthrough point 3|, through a relay coil 32, through one filament 34 ofthe exciter lamp 23, and then to point 33 and returns to point 33 at thepre-amplifler 0. Connected in parallel with the relay coil 32 and thefilament 34 is a second filament 31 in the lamp 23, and a, contact 33,operated by the relay 32. When current flows through the filament 34,the relay coil 32 is energized and the contact 33 is opened. When thefilament 34 burns out and breaks the return circuit of the relay coil32, the contact 33 closes, thereby lighting the filament 31. It is seenthat the relay coil 32 serves as a safety device, and continuesoperation of the electronic frequency generator even though one of thefilaments of the lamp 23 is burned out. The minute current pulsationsgenerated by the photo-electric cell 21 are delivered to thepre-amplifier C through points 11 and 13.

Current from the main A is also delivered through a motor stop and startswitch I30 in closed position thereof to point ill, to the primary of apower input transformer in the power amplifler B, returning to point 92and then to main A.

High voltage circuit When current flows in the primary of this powerinput transformer there is induced in the secondary windings, voltagesnecessary for the operation of the power amplifier Band thepro-amplifier C in the well known manner. These high voltages supplyalternating current that is rectifled through suitable means in thepower amplifier B and applied to the plates of the various vacuum tubesemployed.

With the disc motor 25 revolving the frequency control disc 22, and theexciter lamp 20 focused on to the photo-electric cell 21, and thefilaments and the various vacuum tubes supplied with their propervoltages, it is only necessary to supply high voltages of direct currentto obtain a power output from the power amplifier B, The output powerfrom the power amplifier B flows in the center tapped primary winding ofa power output transformer 90. There is then induced in the secondarywinding between points 94 and 95 a current whose frequency is determinedby' the frequency control disc 22. This current flows from the secondarywinding to points 04 and 91, through the running winding 98 of thesynchronous motor I6 to point I00, and returns to point 95. There isalso a parallel path from the point 01 to point 605 through contact I02in the right hand dotted position shown, to points I03 and 04,

connected long enough to bring the armature almost up to synchronousspeed at the highest frequency. It is also necessary that the startingwinding I I2 be out off after the armature has reached almostsynchronous speed to allow the motor to rotate solely by the effectgenerated by the running winding 98. To apply the current to thestarting winding II2 long enough to bring through a switch I105, throughone of the start- Timing device The motor I6 is of the capacitor starttype requiring one of the condensers I06, I01, I08, 509 in series withthe starting winding I I2, as will be more fully described. When astandard motor of this type is used on a standard commercial frequency,the motor armature is equipped with a centrifugal throw-out switch inthe circuit of the starting winding II2. If a motor has been designed torun at a synchronous speed of 1800 armature revolutions per minute, thenthe centrifugal cutout switch is so designed as to be opened or thrownout at approximately 1200 armature revolutions per minute. In theapplication of this type of capacitor start motor with frequencycontrol, the standard type of centrifugal throw-out switch would not besuitable, as the armature must at times be rotating at synchronousfrequencies as low as 600 revolutions per minute, and as high as 12,000revolutions per minute.

It is common knowledge to those versed in the art that the powergenerated by the starting winding I I2 must be available to bring themotor armature up to nearly'synchronous speed, and the rotatingelectrical field which determines the synchronous rotating speed cf themotor must be allowed to keep the armature in step at this frequency. Itis not important that the starting winding I I2 be cut off electricallyjust before the motor armature attains synchronous speed, but it isnecessary that said starting winding remain the armature up to nearlysynchronous speed at the highest frequency, which may be as high as 400cycles, and cutting it off electrically at this point, there is provideda synchronous timing motor I5, and a cam switch device IIB operated fromsaid timing motor.

The cam switch device IIG comprises three cams 20, I2I, and I22, mountedfor rotation in unison on a shaft I23, driven from the timing motor H5as shown. in Figs. 7 and 8. The earn 820 is adapted to operate a switchI25 to move it into the solid line or dotted line position shown. inFigs. 6 and t, similarly the cams E23 and E22 operate the two switchesI25 and I21. Dur ing one revolution of the three cams I20, 62! and 522,the switch :24 is held in solid line position and against contact 525from 0 to 10, and in dotted line position and against contact 225 from11 to 360; the switch I26 is held "in dotted line or closed positionfrom 355 to 360, and in solidline or open position during the rest ofeach revolution; and the switch I21 is held in dotted line or closedposition from to 255, and in solid line or open position during the restof each revolution.

The cams I20, iii and E22 have projections of the required arcuatelength, that on cam I being very short and extending through 10, asshown in Fig. 8. Each cam projection may engage a spring finger which isalternately pushed up and then dropped, and each spring linger may havea projection to engage and operate its respective switch I124, I 26 or521.

When the motor start and stop switch I30 on the main line A is closed,current is not only rendered available to the power input transformersthrough points 9| and 92 as described,

but current also flows from point I3I, to points 532, I33 and I34,through contact I and switch I24, through the timing motor II5 to rotatesaid motor, to points i38, I31 and 12, and back to the main line atpoint 1I. Switch I24 is closed at contact I25 from 0 to 10duringrotation of the cams. It breaks circuit at contact I25 and closesat contact between 10 and 11. It is of the quick action type, and is soconstructed that it engages either contact I25 or I25 with nointermediate position except during the time required to effect theswitchover. With switch I24 at contact I25, as shown in dotted lineposition, and the circuit of contact I25 opened, the current does nothave to flow through the motor "stop or start switch I30 to continuerotation of the timing motor II5 through the remainder of its timingcycle, but will flow from point 18 on one side of the main A to point15, through the contact I25 and the switch I24 in the dotted lineposition, through the timing motor II5 to points I35, I51 and 12, andthen to the other side of said main.

It is sometimes necessary for thecutting machine operator to move thedrive unit I8 only a short distance. He will accomplish this by closingthe switch I30, and after the motor I8 has just begun to move the driveunit I3, he will immediately open said switch to turn of! said motor.

The mechanical shift of switch I25 from contact I25 to I25 at about 10of cam rotation allows the motor start switch I30 to be opened to stopthe drive motor I 6, yet providing current to be supplied to the timingmotor II to return it to its original 0 position.

Switch I21 supplies current to the'relay coil II 3, and for that purposeis closed from to 255 of cam rotation as described, to provide currentflow through switch I30 to points I3I and I32, through switch I21 inclosed dotted position shown, through relay coil II3, to points I31 and12, and to point H on the main A. The energizetion of the relay coil II3causes closure of the contact I02 in the right hand dotted positionshown, and thereby causes flow of current to the starting winding II2from the secondary of output transformer 93 as already described.

The purpose of switch I25, which is closed from 355 to 360 of camrotation is to energize a timing relay I40 to open the circuit of thetiming motor H5, and thereby allow said motor to rotate only through onetiming cycle. When this switch I25 is closed in dotted position shown,current will flow through switch I to points I3I I32 and I33, throughrelay coil I40 to point I, through switch I25 to points I35, I31 and 12,and to point II on the main line. Relay coil I40 will now becomeenergized closing a contact I42 and opening contact I35 into dottedpositions shown. When contact I 42 is closed, the current does not haveto flow from point I through switch I25, to points I38 and I31 and on topoint H on the main, but flows directly from point I 4I through contactI42, to point I31, and on to point 1| on the main. When contact I35 isopen in dotted position shown, it does not allow current to flow tocontact I25 and switch I24. This switch I24 is away from the contact I25from 355 to 360, while the timing motor H5 is receiving current throughswitch I24 and contacts I25. Thus the timing motor I I5" will continueto rotate until at the end of 360 switch I24 moves away from contact I25and engages contact I25, but due to contact I35 being opened by virtueof the relay I40 being energized, the timing motor II5 will come to restat its normal position, but is ready at any time thereafter to repeatits timing cycles The rotation of the timing motor II5 through onecomplete cycle takes about six seconds.

Switch I21 which controls current to the starting winding H2 is closedfor about four seconds.

That is sufllcient time to bring the armature of the drive motor I 5 tosynchronous speed at the maximum frequency of 400 cycles.

Electrical circuit between rare-amplifier C and power amplifier B Thewiring from the power amplifier B to the preamplifier C consists of anumber of wires, which supply filament voltage and plate voltage for thetubes, and current for the exciter lamp 25, and which are not shownsince these are well known in the art.

A matched impedance line from points I45, I46 on the pre-amplifier unitC, to points I41 and I48 on the power amplifier unit B, carry the outputfrom said pre-amplifier unit and deliver it to the input of said poweramplifier-unit, and might be anywhere from 25 to 100 ft. in length toprovide flexibility of location between said units. r

The use of a matched impedance line is familiar to those versed in theart, and consists of an output transformer I50, connected across pointsI and I45 in the pre-amplifler C. At the other end of the line betweenthe points I 41 and I 45 is the frequencies indicated between points Dand 0.

an input transformer I5I. These two transformers, I50 and I5I are equalin electrical impedance to eliminate any electrical distortion of thewave form.

In inductive electrical circuits employing alternating current, theimpedance of a device drawing power increases with an increase in thefrequency of the supply current. An attempt has been made to maintainthe useful wattage employed by the motor I5 constant at all frequencies. To maintain the current as nearly constant as possible, theapplied voltage must be increased to overcome the increase in impedancecaused by an increase in the frequency, since current is equal to theapplied voltage divided by the impedance of the receiving device.

By means to be described, the voltage is increased with an increase infrequency. In the curve shown in Fig. 9, the abscissa indicatesfrequency generated by the frequency control disc 22, and the ordinateshows the output voltage obtained to operate the synchronous drivingmotor I B. This voltage frequency characteristic follows substantially astraight line as indicated by the lines DE or FG. By an adjustment of acon-.

trol which regulates the amount of amplification in the pre-amplifier C,curve DE rotates about some point 0 to various positions, such as thatshown by the line FG. If this aforementioned amplification control isadjusted so that the output voltage varies with frequency and indicatesvalues as shown by curve DE, then the amount of voltage is suflicient tooperate the motor I6 at the frequencies indicated between points 0 andE, but is not suflicient to operate said motor at If this amplifiercontrol is adjusted to deliver output voltages indicated bythe line FG,then the voltages at the lower frequencies have been raised, but thevoltages for the frequencies between points H" and G'have been lowered,and the motor I5 does not receive voltages powerful enough to operateit. To overcome this difficulty, there have been provided two constantimpedance attenuators I52 and I53, inserted in the line between thepre-amplifier C output transformer I50 and the power amplifier B inputtransformer I5 I, and controlled from a switch I54. These constantimpedance attenuators control the coupling between transformers I50 andI5I, yet maintain the proper impedance relationship, and keep these twotransformers electrically balanced at all times to avoid distortion ofthe wave form.

The attenuator I52 is effective to produce the voltage frequencycharacteristics indicated by the curve FH for the lower range offrequencies, as for instance up to 200 cycles, while the other attenuator I 53 is designed for effective operation above this frequencyrange up to 400 cycles to produce the voltage frequency characteristicsin-- dicated by the curve 1E. By switching the attenuator I52 or theattenuator I 53 into the circuit at the proper time through operation ofthe switch I54, the characteristic indicated by the heavy lines FH or IEis obtained. g

The operation of switch I54 is performed by the same mechanism thatshifts the exciter lamp 25 and photoelectric cell 21 to selectiveannular rows on the frequency control disc 22. For that purpose theswitch unit I54 is operated from a ,with the nut 45 is adapted to rideover the roller I51 when said nut reaches a position corresponding to acontrol setting of above 200 cycles. In this position lever I58 pushesthe plunger I55,

and thereby operates the switch I54 to cut out the Fig. 2, so that theattenuator I52 will be cut in and 'the other attenuator I53 cut out toproduce the voltage frequency characteristics indicated by curve FH.

Means ,for regulating the magnitude of the output voltage When theswitch I30 is closed to start the synchronous driving motor I0, currentwill flow from point at to points 96 and 91, through the motor runningwinding 98, to point I00, and returns to point 95. Current also flowsfrom point 31, to point IOI. It is assumed that motor I6 is just beingstarted, so that relay coil H3 will become energized for the duration oftime necessary to provide current through the starting winding I I2.When relay coil H3 is energized, contact I02 is closed in dottedright-hand position shown in Fig. 6, which means that current continueson a path from point III, through said contact, to point I03,. and onthrough the starting winding I I2, eventually returning to point 05.

Points 35 and I55 are groimded, so that the voltage between points I05and 05 is found equal to that between points Si and 95. A slightly lowervoltage exists between points I65 and I, and a still lower voltagebetween points I55 and I51.

A condenser I53 is connected across the points I65 and I51. It is a wellknown action of condensers in alternating current circuits, that theirimpedance decreases with an increase in frequency. Therefore if thefrequency generated by the frequency control disc 22 is raised, thevoltage between points I55 and I01 will be lowered, and if the frequencyis lowered, the voltage between points I55 and I51 will be raised.

This condenser action is utilized by use of a triode rectifying vacuumtube I10, which allows negligible current to flowthrough it inone'direction only. The output from this tube I at point "I fiows fromthis point to point I12 and up to the pre-amplifier C, to control theamountof amplification of the pre-amplifier B. The voltage obtainable inthis manner from point I1I is applied to a control grid of one of theamplifying tubes in the pre-amplifier C, and controls the output voltagein such a manner that the output voltage is proportional. to itsfrequency. This automatic device regulates the overall amplificationvalue of the pre-amplifler in such a. manner that the output voltage isalways the correct value for each operating frequency. I

It is desirable to employ a slightly higher voltage ontbe drive motor I3during the starting period. For that purpose there is provided aresistor I between points 35 and I55, and a contact I13, which when clamshort circuits this resistor. A contact I1 is pivotally supported at itsbase between the contacts I32 and I13, and is operated from the relaycoil III to close or open said contacts. This contact I13 will alway beclosed when relay coil 3 is not energized.

During part of the timing cycle, the relay coil II: is energized, sothat the contact I13 across the resistance I15 will be open. With thiscontact I13 open, the percentage of voltage drop between points I55 andIE1 will be lowered. and the I contact I13 is closed, so that resistorI15 will be short-circuited, and the actual output voltage lowered.

Switching means for starting condensers The synchronous driving motor I5is of the capacitor start type, requiring a starting condenser in serieswith the starting winding I I2. The purpose of this condenser is toobtain an amount of electrical shift of the phase, depending upon thefrequency of the applied current and the capacity of said condenser.

With the wide range of frequencies employed in operating motor I8, itwas found that the higher the frequency, the lesser the capacityrequired. For synchronous motor operation from 20 to 400 cycles, it wasfound that four condensers I06,

I01, I00 and I09 of different capacity are required to cover this rangeof frequencies. For instance, condenser I06 has proper capacity forfrequencies from about 20 to cycles per second; condenser I01 forfrequencies of about 100 to 200 cycles; condenser I00 for frequencies ofabout 200 to 300 cycles; and condenser I09 for frequencies of about 300to 400 cycles.

The proper condenser is connected in series with the starting winding II2 by the same mechanism, which shifts the exciter lamp 25 andphotoelectric cell 21 into registry with a selected row of the frequencycontrol disc 22. For that purpose four terminal strips I00, IIII, I32and I83 connected to condensers I05, I01, I08 and I09 respectively aremounted alongside of each other as shown in Fig. 2, while a conductorstrip I84 is mounted below said terminal with one end corresponding topoint I04. Rigid with the arm 41 are a pair of switch blades I05 and I05carrying brushes riding in electrical contact with the upper and lowerstrips, and serving to connect the proper condenser in series with thestarting winding II2.

To generate three phase alternating current three identical frequencycontrol discs would be mounted on the same synchronous motor shaft. Eachdisc would be provided with a light source and photo cell combination,but with all three lamps and photo-electric cells mechanically tiedtogether. If the light focused on the first control disc was justcommencing to pass throush the light transmitting section and on to thefirst photo-electric cell, then the second control disc would be soarranged that it would be one-third of a cycle behind the first disc,and the third disc would be one-third of a cycle behind the second disc.With three separate frequency con- 1 trol discs and three separateamplifier units, it is possible to generate three alternating currentswhose phase relationship has been determined by widely differentembodiments of this invention could be made without departing from thescope of the claims. it is intended that all matter contained in theabove description or shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A torch cutting machine having a movable carriage, a tracing unit anda torch, both supported on'said carriage, and connected together formovement crosswise of the movement of said carriage, a synchronous motorfor driving said tracing unit, and means for generating current ofdifferent frequencies and delivering it to said motor to operate saidmotor at selected speeds.

2. A torch cutting machine having a movable torch, a synchronous motorfor moving said torch over a plate to be cut, means for deliveringalternating current to said motor to drive said motor, and means forchanging the frequency of thecurrent delivered to said motor inaccordance with th thickness of the plate to be cut.

3. A torch cutting machine having a movable torch, a synchronous motorfor moving said torch, a movable control member, and means automaticallyresponsive to changes in'the position of said control member, forgenerating'alternating current of selected frequencies corresponding tothe position of said control member, and delivering it, to said motor tooperate said motor at a speed corresponding to the selected frequency.

4. In a torch cutting machine, the combination of a movable torch, asynchronous motor for driving the torch at cutting speed over the plateto be cut, means for generating periodic current pulsations at selectedfrequencies depending on the desired cutting speed, means for amplifyingsaid current pulsations to a value necessary to operate said motortherefrom, and means for delivering said amplified current pulsations.to said motor to operate said motor at the desired speed.

5. A torch cutting machine having a movable torch, a drive unit for thetorch comprising a synchronous motor for moving said torch over thework, an indicator device indexed with a tabulation of differentthicknesses of plate to be cut, and means automatically responsive tothe setting of said indicator device to any selected index forgenerating currents for said motor of a frequency corresponding to theproper cutting speed for the plate thickness selected on said device.

6. In a torch cutting machine, the combination of a movable torch, asynchronous motor for moving said-torch over a plate to be cut, a chartshowing different thicknesses of plate to be cut, an indicator devicemovable over said chart, means automatically responsive to the settingof said indicator device to any selected point on said chart forgenerating periodic current pulsations at selective frequenciescorresponding to proper cutting speed for the plate thicknesses selectedon safd'device, means for amplifying said current pulsations to a'valuenecessary to operate said motor therefrom, and means for delivering saidamplified current pulsations to said motor to operate said motor at thedesired speed.

7. A torch cutting machine including'a movable torch, a synchronousmotor for driving the torch at a cutting speed over the plate to be cut,means for generating current pulsations of different frequencies, andincluding a movable control member having a plurality of rows ofconformations controlling the frequency of said pulsations, and meansfor selecting any one of said rows for operation to obtain current ofcorresponding frequency. means for amplifying said current pulsations toa value necessary to operate said motor therefrom, and means fordelivering said amplified current pulsations to said motor to operatesaid motor at thedesired speed.

8. A torch cutting machine including a movable torch, a synchronousmotor for driving the torch at cutting speed over the plate to be cut, amember for generating current pulsations, a rotatable control dischaving annular concentric rows of conformations for determining thefrequency of the current. pulsations generated by said member, saidfrequency being determined by the positioning of said member withrespect to said rows, means for adjustably moving said member relativelywith respect to said disc to correspondingly change the frequency of thegenerated current pulsations, means for amplifying said currentpulsations to a value necessary to operate said motor, and means foroperating said motor from the amplified current.

9. In a torch cutting machine, the combination comprising a movabletorch, a synchronous motor of the capacitor start type for driving thetorch at a cutting speed over the plate to be cut, a plurality ofcondensers of different capacity, each suitable for a different range offrequency of the motor operating current, means for generating currentof selected frequencies and impressing it on said motor to operate saidmotor at selected speeds, control means for selecting the frequency ofthe current to be generated, and switching means automatically operableupon the setting I of the control means to a selected frequency forconnecting the proper corresponding condenser in the circuit o thestarting winding of said motor.

10. In a torch cutting machine, the combination comprising a movabletorch, a synchronous motor for driving the torch at a cutting speed overthe plate to be cut, means for generating current pulsations of selectedfrequency, means,

for amplifying said pulsations to a value neces# sary to operate saidmotor, and including a pair of constant impedance attenuators, eachdetermining a different output voltage frequency-characteristic, one ofsaid attenuators being suitable for the lower range of frequency, andthe other attenuator for the higher range, control means for selectingthe frequency of the current to be generated, and means automatically;operable upon the setting of the control means to a selectedfrequencyfor switching into operation the constant impedance attenuator suitablefor the selected frequency, to obtain the desired output voltagefrequency characteristic.

11. In a torch cuttin machine. the combination comprising a movabltorch, a synchronous motor for driving the torch at a cutting speed Iover the plate to be cut, and including a starting winding, means forgenerating current of selected frequencies and delivering it to saidmotor to operate said motor at selected speeds, and means for deliveringcurrent to said winding for a predetermined period, and automaticallydisconnectin said winding from said current at the end of said period,irrespective of the frequency of the motor current, to bring the motorarmature up to nearly synchronous speed.

CHESTER MOT'I.

ALFRED F. .CHOUINARD.

